Why console.log Can Mislead JavaScript Developers During Debugging
Browser DevTools does not immediately serialize objects passed to console.log; instead, it stores a live reference and renders the value only when the user expands the entry. This behavior, known as lazy evaluation, means the console displays the object's current state at inspection time, not its state at the moment of logging. As a result, if an object's properties are mutated after the log call, the expanded view will reflect the updated values rather than the original ones. The same issue affects Promises, which may appear as 'pending' when logged but show as 'fulfilled' once expanded after resolution. This design is intentional, as eager serialization of every logged object would impose significant memory and performance costs in complex applications.
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